Use of clay in systems containing vinyl monomers

ABSTRACT

A SMALL AMOUNT OF A POLYOXYETHYLENE FATTY ACID ESTER IS COATED ON A DRY CLAY FILLER HAVING SURFACE ACIDITY. WHEN INCORPORATED WITH AN ETHYLENICALLY UNSATURATED MONOMER, UNDESIRED POLYMERIZATION OF THE MONOMER BY THE CLAY IS PREVENTED.

United States Patent 3,594,204 USE OF CLAY 1N SYSTEMS CONTAINING VINYLMONOMERS John C. Nease, Piscataway, N.J., assignor to Engelhard Minerals& Chemicals Corporation, Edison, NJ.

No Drawing. Application Sept. 8, 1967, Ser. No. 666,491, now Patent No.3,450,666, dated June 17, 1969, which is a continuation-impart ofapplication Ser. No. 457,176, May 19, 1965. Divided and this applicationApr. 4, 1969, Ser. No. 842,039

Int. Cl. C09c 1/00 U.S. Cl. 106288B 6 Claims ABSTRACT OF THE DISCLOSUREA small amount of a polyoxyethylene fatty acid ester is coated on a dryclay filler having surface acidity. When incorporated with anethylenically unsaturated monomer, undesired polymerization of themonomer by the clay is prevented.

RELATED APPLICATION S' This application is a division of my copendingapplication Ser. No. 666,491, filed Sept. 8, 1967, now U.S. 3,450,666,which in turn was a continuation-in-part of a copending application Ser.No. 457,176, filed May 19, 1965, now abandoned.

BACKGROUND OF THE INVENTION It is well known that clays, especiallyacidic clays, catalyze the polymerization of liquid vinyl monomers suchas styrene when the clay is dry. The reaction between clay and monomeris accelerated when the monomer is warm or hot and occurs even whenconventional polymerization inhibitors such as tertiary butyl catecholor hydroquinone are present. The patent literature contains manysuggestions for putting this phenomenon to practical use. An example isUS. 2,644,722 to Kaye. In accordance with the procedure described inthis patent, an object such as mica is rapidly provided with a solidresinous surface coating by coating the surface of the object with vinylmonomer and clay. The latter remains as a filler in the coating afterthe polymerization of the monomer occurs.

While the exothermic reaction between the clay and the resin-formingpolymerizable liquid in very desirable for certain applications, such asthe one described, the reaction is very undesirable when it occurs insystems in which it interferes with the normal catalysis of apolymerizable monomer by a free radical initiator catalyst such as anorganic peroxide. In this case, the reaction between clay andunsaturated monomer can lead to shortened pot life or to impairment ofthe physical properties of the cured clay-filled plastic. An example iswhen kaolin, an acidic clay, is used at a filler for a liquid polyesterresin containing a vinyl monomer as the crosslinking agent. Reactionbetween clay and the crosslinking agent can have a detrimental effect onpot life or the properties of the finished plastic. The reaction betweenthe clay and the ethylenically unsaturated monomer can be prevented orminimized by using moist clay. However, this means is not alwayspractical or possible. For example, filler clay must be pulverized inorder to facilitate the dispersion of the clay in an organic system;e.g., the clay must be free from agglomerates coarser than about 100mesh. It is impossible, however, to pulverize moist clay because of theinherent plasticity of the moist clay. Moreover, the clay equilibrateswith the atmosphere, and clay which is adequately moist and nonreactiveafter it has been pulverized may rapidly dry and become reactive whenstored in a dry environment.

3,594,204 Patented July 20, 1971 ice,

An object of this invention is the provision of a means for preventingthe reaction between clay and an ethylenically unsaturated monomernormally polymerizable by the clay.

A particular object of this invention is the provision of a coated clayproduct which is especially adapted for use in resin systems includingmonoethylenically unsaturated monomers.

Another object is to provide a coated acidic clay product which isessentially inert towards a polymerizable monoethylenically unsaturatedmonomer.

This invention results from the discovery that a small amount of apolyoxyethylene fatty acid ester prevents the reaction between clayshaving surface acidity and ethylenically unsaturated monomers. Thecompounds which are used to prevent the reaction, in accordance with thepresent invention, are nonionic surface active agents prepared byreacting a fatty acid with an alkoxylating agent, such as ethylene oxideor polyethylene glycol.

In accordance with this invention, the polyoxyethylene fatty acid esteris employed in amount of /2% to 5% of the clay weight and may beincorporated as a precoating on the dry clay before the clay isincorporated into a solid or a liquid including an unsaturated monomernormally polymerizable by the clay or the ester may be added to thesystem containing the monomer before clay in added.

Using the preferred kaolin clay, which is an excellent filler clay butwhich is very reactive when dry, the surface active agent is employed inamount within the range of /2% to 3% of the clay weight. With moreabsorptive clays, such as heat-activated attapulgite clay, which isanother clay material having acid sites on the surface of the clayparticles, the nonionic agent can be sed in amount of 2% to 5% of theclay weight. The presence of the ester as a coating on the clay or inmixture with the monomer system inhibits the normal reaction between thefiller clay and a polymerizable monomeric monoethylenically unsaturatedmonomer. When employed as a coating, the ester also improves the easewith which the clay can be incorporated into liquid systems used informulating plastics. Thus, the coated clays disperse readily in organicvehicles without undesirably increasing the viscosity of the vehicles.

The present invention finds application in the preparation ofclay-filled polyester plastics from liquid unsaturated polyester resinmixes containing vinyl monomers as the crosslinking agent. As examplesof vinyl monomers may be mentioned styrene, vinyl toluene, chlorostyreneand/or alphamethyl styrene. The use of a surface active polyoxyethylenefatty acid ester with clay filler, in accordance with this invention,obviates premature reaction between the clay and the monomericcrosslinking agent. With some laminating resin mixes, this will preventsurface blistering and/or delamination of the cured clay-filledlaminate. In all cases, this will lengthen pot life.

The invention is also applicable to the preparation of plastics fromliquid resins including a substantial amount of liquid polymerizablemonomeric monoethylenically unsaturated compounds. For example, the useof the polyoxyethylene fatty acid ester prevents reaction of clayfillers used in the preparation of polystyrene plastics and acrylicplastics from styrene monomers and acrylic monomers, respectively. Theesters also prevent reaction of clay fillers with polystyrene orpolyacrylates containing unpolymerized styrene or acrylic monomers.

The following are examples of polymerizable monomeric monoethylenicallyunsaturated compounds normally polymerized by contact with clay havingacid sites: Styrene, nuclearly halogenated styrene, alkylated styrenesuch as alpha-methylstyrene, vinyl chloride, vinyl fluoride, vinylidenechloride, di-vinyl benzene, vinyl toluene; vinyl esters such as vinylacetate and vinyl trimethylacetate; vinyl ketones such as vinyl methylketone and vinyl propyl ketone; also acrylic and alphamethacrylic acidsand derivatives thereof, such as esters, amides, nitriles, chlorides andanhydrides and including acrylonitrile, methacrylonitrile, allylacrylate and methacrylamide. Frequently combinations of theaforementioned polymerizable monomers are employed when they arecopolymerizable.

The polyoxyethylene fatty acid esters which are employed in the practiceof this invention may be represented by the following formula:

wherein R is selected from the group consisting of alkyl containing 7 to19 carbon atoms, alkenyl containing 7 to 19 carbon atoms and abietyl,and x is an integer from 2 to 50, inclusive. The esters may be made frompure acids, such as oleic acid or lauric acid, or naturally occurringfatty acid mixtures such as coconut fatty acids, tall oil acids, soybeanacids may be used. Especially good results are obtained with liquidesters derived from acid mixtures such as coconut fatty acids whichcontain a substantial amount of C-12 fatty acid and which contain to 15mols of ethylene oxide per mol fatty acid.

The polyoxyethylene fatty acid esters used in practicing the inventionare liquid or pasty at ambient temperature. The esters therefore areeasy to coat on the clay filler or to incorporate uniformly with themonomer to be protected. When employed in amount sufficient to preventpolymerization of a monomer by the clay, this type of surface activematerial does not interfere with the subsequent polymerization of themonomer by a peroxide catalyst. Further, the ester does not containnitrogenous constituents which may be undesirable when present inpolymerizable systems.

Any clay filler material that normally catalyzes the decomposition of anethylenically unsaturated monomer of the type above-described can beused in carrying out this invention. A characteristic of such clays isthat acid sites are present on the surface of the clay particles. Thepresence of these sites is determined by pK measurements. The surfaceacidity may be readily measured by the method of Walling, Cheves, J. Am.Chem. Soc., 72, pp. 1l6468 (1950), which depends upon the ability of theclay to change a neutral-base color indicator to its acidic color.Reactive clays have a pK below 3.3 and highly reactive clays such askaolin and attapulgite have a pK less than 1. Another characteristic ofthese clays is that they are dry, i.e., the clay particles contain lessthan 1% free moisture (F.M.). Free moisture is the weight percent of amaterial eliminated by heating the clay material to constant weight at220 F. While low in free moisture, the reactive clays may containappreciable quantities of chemically combined water (water ofcomposition or water of crystallization).

Still another characteristic of the clays that are benefited by the useof a polyoxyethylene fatty acid ester, in accordance with thisinvention, is that the clays are free from additives that willfundamentally change the natural surface characteristics of the clay ina manner such as to react with or mask the acid sites on the clay. Asexamples of such additives, present with some commercial clays, may bementioned clay dispersants such as alkali metal salts of condensedphosphates and alkali metal silicates. If present in substantialquantity, these alkaline dispersants, which may undesirably affect curedresins, neutralize acid sites on the clay. Another type of additive isone that provides a hydrophobic, or partially hydrophobic coating on theclay. To distinguish the clays I use from the commercially processedclays containing such additives, one group of the clays employed incarrying out this invention and used as filler clays, can be describedas being processed, but unmodified clay. Thus, the term processedunmodified'clay as used herein excludes predispersed clays andhydrophobic clays. As examples of processed, unmodified clays which havebeen found to catalyze the decomposition of ethylenically unsaturatedmonomers the following may be mentioned: kaolin clay, includingwater-washed aid air-floated kaolin clays; ball clay; Wyoming bentonite(a sodium montmorillonite); calcium bentonite (a calcium montmorillonitefrom Arkansas); a commercial grade of colloidal attapulgite dried to afree moisture content below 1%; a heat-activated grade of attapulgiteclay having a free moisture content below 1%.

The other group of dry clays having acid sites that is benefited by theuse of the polyoxyethylene fatty acid esters is that of theacid-activated clays, exemplified by acid-activated kaolin clay andsub-bentonites, such as are widely used as catalysts in the cracking ofhydrocarbons. A method for acid-activating kaolin clay is described inUS. 2,967,157 to Alfred J. Robinson et al. Methods for acid-activatingbentonite are described in US. 2,466,050 to Hubert A. Shabaker et al.

The preferred clay that is employed in carrying out this invention iskaolin clay, by which is meant a clay whose predominating mineralspecies is kaolinite, halloysite, anauxite, dickite or nacrite. Theseminerals are all hydrous aluminum silicates of the empirical formula AlO -2SiO 2H O. Kaolin clay, as mined, consists of fine particles togetherwith coarse agglomerates and grit (principally quartz). It is the usualpractice of clay processors to remove from the clay coarse agglomeratesand gritty matter. For some commercial uses, kaolin clay isfractionated, as by hydraulic or air sedimentation methods, to obtain afraction of clay having the desired particle size. Usually the clay isfractionated to obtain a very fine fraction which is particularly usefulas an ingredient of paper coating compositions. This leaves a coarsefraction, the particle size distribution of which will depend on theamount of fines removed from the whole clay during the fractionation. Incarrying out my invention, I prefer to use a coarse fraction size ofclay which has an average equivalent spherical diameter from 4 to 15microns. Whole clay (which usually has an average equivalent sphericaldiameter of about 1.5 micron) and fine fractions of whole clay can alsobe used. It is also within the scope of this invention to employ kaolinclay which has previously been calcined. All micron particle sizes, asused herein, are expressed as equivalent spherical diameters and areobtained by the well-known Andreasen method (a Water sedimentationmethod) assigning 2.5 as the value of particle density. The term averageequivalent spherical diameter refers to the particle size of a materialwhich is so chosen that 50% by weight of the particles will be finerthan that value.

Another clay that could be used in carrying out this invention isattapulgite clay which has been heated at a temperature and for a timesufficient to reduce the free moisture content below about 1% by weight,e.g., the heat-activated grades of attapulgite clay which have beenheated at a temperature within the range of about 400 F. to 1300 F. Thisclay, while it normally has a pH about 7, is considered to be an acidclay because it has acid surface sites which are detected by pKevaluations.

Several methods may be used to precoat clay particles with the estercompounds. The simplest procedure involves dry milling the clay with anappropriate quantity of surface active agent. This method is suitablebecause the esters are normally liquid or semiliquid (pasty) at ambienttemperature. The esters are easily coated on the clay particles becauseof their low melting points without the need for solvents and the use ofa drying step although solvents such as mineral spirits may be used inthe coating step.

With kaolin clay, the polyoxyethylene fatty acid ester is employed inamount within the range of about /2% to 3%, preferably about 1% to 2% ofthe clay weight. When employed in amount appreciably less than /2% byweight, reaction may occur between the clay and monomer. When employedwith kaolin clay in amount appreciably in excess of 3%, the surfaceactive agent may undesirably affect the properties of the resins withwhich the kaolin clay is employed. With activated attapulgite clay andother high surface area clays, somewhat larger quantities ofpolyoxyethylene fatty acid esters are recommended, i.e., from about 1%to 5% by weight, preferably about 2% to 4% by weight. The optimumquantity of surface active agent employed with a clay material will varyinversely with the particle size and surface area of the clay. Thequantity of polyoxyethylene fatty acid ester will usually be kept at theminimum at which the agent is effective in preventing polymerization ofthe monomer by the clay since the use of excessive polyoxyethylene fattyacid ester may adversely affect the physical properties of the curedresin system.

The liquid unsaturated polyester resins to which the practice of thisinvention is applicable are obtained by reacting together a dihydricalcohol and a dibasic acid, either of which contains a pair ofdouble-bonded carbon atoms. The unsaturated long chain polyestermolecule is essentially linear and is capable of being crosslinked toform a thermosetting resinous solid through the double bonds in theester. A liquid unsaturated monomer, such as styrene, vinyl toluene,alpha-methyl styrene, chlorostyrene or mixtures thereof, is employed asa crosslinking solvent, and an organic peroxide is usually employed tocatalyze the crosslinking reaction. The unsaturated polyesters arecharacterized by thermosetting without evolution of water. Commericialunsaturated polyester resins usually contain a mixture of unsaturatedpolyesters and unsaturated monomeric solvent.

Polyols used in the preparation of commercial polyesters include:ethylene glycol, propylene glycol, various butylene glycols, diethyleneglycol and triethylene glycol.

Maleic anhydride or phthalic anhydride and fumaric acid are the mostfrequently used unsaturated acids in the preparation of unsaturatedpolyesters. Other suitable unsaturated acids are citraconic acid,messconic acid, itaconic acid and 3:6 endomethylene tetrahydro phthalicanhydride. Equimolar proportions of glycol and dibasic acid are usuallyused. The unsaturated acid is frequently modified with other dibasicacids, usually phthalic acid or anhydride, sebacic acid and adipic acid,to improve the flexibility of the thermoset product. In some instancestrihydric alcohols, such as glycerine, or esters such as castor oil, orhigher alcohols, such as pentaerythritol or sorbitol, are used to modifythe product.

As mentioned, the crosslinking reaction is catalyzed with a peroxidecatalyst, usually benzoyl peroxide. Other catalysts are methyl ethylketone peroxide and methyl isobutyl -ketone peroxide.

Accelerators, stabilizers, promotors and coloring agents may beincorporated in the polyester when desired, as well as reinforcingagents, such as glass or sisal, and auxiliary fillers such as fibrousasbestos, calcium carbonates, etc.

In the preparation of moldable polyester mixes employing the novelcoated kaolin, the clay is added to the unsaturated liquid polyesterresin in the same manner and with equipment usually employed for addingclay or other fillers to the resin.

The quantity of clay that is used is usually within the range of from to50%, based on the weight of the liquid unsaturated polyester (inclusiveof the polymerizable monomer, such as styrene).

After the ester and clay are dispersed in the liquid polymerizableunsaturated monomer and catalyst added, the mixture is placed in asuitable mold and cured in a manner applicable to the particularpolyester resin employed.

In practicing the embodiment of my invention in which thepolyoxyethylene fatty acid ester and clay filler are incorporatedseparately into a system such as polyester or polystyrene which containsa clay-reactive monomer, the liquid polyoxyethylene fatty acid ester isstirred into the reactive system before the clay is added. Substantiallythe same proportion of polyoxyethylene fatty acid ester to clay isemployed as when the ester is precoated on the clay. After the clay isadded, conventional catalyst may be incorporated.

The following examples are given to illustrate the invention and to showthe advantage thereof.

Example I The following nonionic surface active agents were coated onkaolin clay and the coated clays were mixed with styrene monomer. Thepresence or absence of reaction of the coated clays with the styrene wasnoted. A control kaolin clay, uncoated, was tested in the same manner.In each case, the clay employed was ASP 400 P, a water-washed Georgiakaolin having an average equivalent spherical diameter of 4.8 micronsand a free moisture content below 1%. The pH of the clay, as determinedby TAPPI Tent. Std. T645 M-54, was 3.8-4.6.

All coated clays were prepared by adding the dry, minus 325 mesh clay toa twin-shell blender (V-Blendor) and tumbling without addition of liquidfor 10 minutes. The surface active agent was diluted in about equalparts by weight with a solvent (mineral spirits) and then introducedinto the twin-shell blender. The mixing was continued for fiveadditional minutes and the minus 325 mesh product discharged. The coatedclay was employed without removing the mineral spirits solvent.

Reactivity was tested by warming 20 cc. of styrene in an aluminum cup ona hot plate maintained at 250 F. and adding 2 grams of clay to the warmstyrene monomer. The styrene monomer that was employed in the testcontained about 50 ppm. of tertiary butyl catechol as an inhibitor.After addition of the clay to the liquid monomer, the system wasobserved continuously for three minutes. When reactive with the monomer,reaction occurred substantially instantaneously and was very vigorous,causing polymerization and hardening of the monomer. The test wascarried out with warm styrene monomer to permit rapid evaluation ofreactivity since the rate of reaction is increased substantially byheating the monomer. A clay which would react immediately with thestyrene monomer under the test conditions employed would react atambient temperature with the monomer given sufficient time. A clay whichreacted immediately under the test would then be expected to interferewith the normal free radical catalyzed polymerization of the monomer.

The results, summarized in table form, show that nonionicpolyoxyethylene fatty acid esters prevented reaction between the dryclay and styrene monomer when the esters were precoated on the clay. Theresults show also that nonionic surface active agents that did notcontain polyethoxy groups were ineffective in preventing reactionbetween the clay and the monomer.

EFFECT OF NONIONIC SURFACE ACTIVE AGENTS AS Polyethoxylated nonionicsurface active clay coating agent Reaction between clay and monomerComposition of surface Trade name active agent No coating on clayViolent reaction within 1 minute.

Ethofat C25 Ethoxylated coco-fatty acids None.

having 15 mols ethylene oxide/incl. acid. Ethoiat 60/25- Ethoxylatedstearic acid having Do.

5 mols ethylene oxide per mol acid.

Nonpolyethoxylated nonionic surface active agents Span Sorbitanmonooleate Violent reaction within 1 minute.

Atpet 200 Sorbitan partial fatty ester Do.

7 Example II In a typical application of this invention, a coarse sizefraction of kaolin filler clay (pH about 4.0 and K, below 1) is mixed ina cement mixer with 1% by weight of Ethofat C25. The mixture ispulverized in a Mikro- Pulverizer (a high speed hammer mill) untilsubstantially all the material is minus 325 mesh (Tyler) when analyzedby a wet-screen method.

A polyester resin molding is prepared with the coated clay filler asfollows. The coated clay is mixed in amount of 29 parts by weight with63 parts by weight of a polyester prepared by esterification of ethyleneglycol with fumaric acid and 7 parts by weight of a styrene monomer. Thecatalyst, benzoyl peroxide, is added in amount of 1 part by weight andthe mixture is molded with fiberglass reinforcement in a hydraulic pressusing matched metal molds. The part is cured for four minutes at 250 F.

Example III Still in accordance with this invention, a fluid energymilled, colloidal grade of attapulgite clay (Attagel 40) is dried atabout 150 F. to a free moisture content below 1%. The clay is uniformlycoated with 3% by weight of Ethofat /15 which is the condensationproduct of ethylene oxide with oleic acid having 5 ethylene oxide molsper mol oleic acid. The mixture is pulverized to minus 325 mesh in ahigh speed hammer mill and employed with a laminating mixture of thefollowing composition to make a fiberglass-reinforced panel.

Parts by weight Polyester resin 76.5 Styrene monomer 8.5 Benzoylperoxide 1.0 Coated attapulgite filler 14.0

Example IV The following tests were carried out to demonstrate theelfectiveness of a polyoxyethylene fatty acid ester in preventing thepolymerization of an ethylenically unsaturated monomer as a result ofcontact therewith of a clay having acid sites by incorporating the esterwith the monomer before adding the clay to the monomer.

To 150 parts by Weight of warm styrene monomer, 0.45 part by weight ofEthofat C25 was added dropwise. The ingredients were mixed thoroughly.Dry ASP 400P was gradually added in amount of 150 parts by weight. Noreaction occurred.

The procedure was repeated except that a fatty acid ester ofpolyoxyethylene glycol was not incorporated into the styrene before theclay was added. In this case, a vigorous reaction occurred and themonomer polymerized and hardened.

It was thus demonstrated that the Ethofat C-25 was effective inpreventing polymerization of the monomer as a result of contact with theclay when the ester was added to the monomer before the clay was added.

I claim:

1. A dry clay having acid surface sites, the particles of said claybeing coated with from to 5% by weight of a polyoxyethylene fatty acidester of the formula:

wherein R is selected from the group consisting of alkyl containing 7 to19 carbon atoms, alkenyl containing 7 to 19 carbon atoms and abietyl,and x is an integer from 2 to 50, inclusive.

2. The composition of claim 1 wherein said clay is kaolin and said esteris present in amount within the range of to 3% of the clay weight.

3. The composition of claim 1 wherein said clay is kaolin and said esteris present in amount of about 1% of the clay weight.

4. The composition of claim 1 wherein said clay is minus 325 mesh kaolinclay having a free moisture content below 1% and being substantiallyfree from clay dispersants.

5. The compression of claim 4 wherein said kaolin clay is coated withfrom to 3% by weight of the coconut fatty acid ester of polyoxyethyleneglycol containing from .5 to 15 polyoxyethylene groups.

6. The composition of claim 1 wherein said clay is attapulgite clay.

References Cited UNITED STATES PATENTS 3,067,053 12/1962 Tarantino106-308O 3,094,499 6/1963 Gassmann et a1. 106308O 3,278,479 10/1966Ferrigno 106308O 3,425,980 2/1969 Baum 106-3080 JAMES E. POER, PrimaryExaminer U.S. Cl. X.R. 106308Q

